Between the years 2000 and 2010 a captive musk ox (Ovibos moschatus moschatus) herd at the Assiniboine Park Zoo experienced morbidity and mortality attributable to the liver fluke Fascioloides magna. In that time period six adult animals from the herd died or were euthanatized, with five of six showing marked pathologic changes due to the presence of this parasite. Postmortem findings on all five affected animals included moderate to severe hepatic changes characterized by hepatic migration tracts with resulting fibrosis, hepatic hemorrhage, and accumulation of hepatic iron porphyrin. Other pathologic lesions consistent with this parasitic infection that presented variably in the affected population included bile duct hyperplasia, anemia, peritonitis, and clotting defects. In 2009–2010 two musk ox from this herd presented with vague clinical signs that resolved following treatment with triclabendazole at an estimated 12 mg/kg (Fascinex 10%, Novartis Santé Animale, Rueil-Malmaison, France) for presumed fluke infestation. Bloodwork for these two animals showed hypoalbuminemia and moderate increases in serum AST and GGT. It is concluded that musk ox are susceptible to morbidity and mortality attributable to the liver fluke Fascioloides magna, and prevention and treatment are warranted in captive populations that may be exposed to this parasite.